Ординатура / Офтальмология / Английские материалы / Atlas of Confocal Laser Scanning In-vivo Microscopy in Opthalmology - Principles and Applications in Diagnostic and Therapeutic Ophtalmology_Guthoff, Baudouin, Stave_2006

membrane. From there, the nerve fibers travel vertically as far as the subbasal nerve plexus,before finally ascending into the upper epithelial layers [61].

Photorefractive keratectomy (PRK) involves ablation of the densely innervated epithelium, the branched subepithelial nerve plexus, and the anterior stroma. In the LASIK procedure, the microkeratome separates the subbasal nerve fiber bundles and the nerves of the anterior stroma along the flap region.

Fig. 5.51 Innervation after refractive surgery. Two years after laser-assisted in situ keratomileusis, there is still rarefaction of the subepithelial nerves, with short and unbranched nerve fibers

Degeneration of nerve structures in the flap vicinity can be detected on confocal microscopy just a few hours after LASIK, as reflected in rarefaction of the subbasal and stromal nerves (Fig. 5.49).

According to Donnenfeld et al.,transection of both arms of the corneal nerve plexus following creation of a superior-hinge flap leads to more pronounced loss of corneal sensation and more pronounced dry eye signs and symptoms than with a nasal-hinge flap [13]. The same phenomenon has been reported with a narrow nasal hinge flap compared with a wider hinge flap in which more nerve fibers are left undamaged [14].

The onset of corneal nerve regeneration appears to occur early. Thus, Linna et al. were able to demonstrate gentle nerve regeneration 1 week after LASIK. Central corneal sensation was restored after 6 months. However,even after 6 months, short unconnected subbasal nerve fibers were still found, in contrast with long interconnected nerve fibers in a control population [44] (Fig. 5.50). Rarefied subbasal nerve fibers of this kind can still be detected 2 years after LASIK (Fig. 5.51). In addition, morphological changes have also been found in the area of the anterior stromal nerves or in the flap region [42] (Fig. 5.52). Using refractive corneal surgery as an example, confocal microscopy is thus able to provide a direct comparison between innervation detectable on microscopy and the sensitivity or symptom severity of the dry eye.

5.3.2.2

Reinnervation After Penetrating Keratoplasty

Corneal innervation is the cornerstone of the normally functioning cornea. Although reinnervation processes have formerly been discussed in the literature, no suitable model was previously available. Different investigators [50, 71, 72, 76, 90] have used a Cochet–Bonnet esthesiometer to estimate graft innervation. Most studies have failed to differentiate between the peripheral and central sensitivity of the corneal graft. The results of these studies are summarized in Table 5.1.

Tervo et al. have demonstrated histochemically that complete regeneration does not occur ei-

ther in the subepithelial nerve plexus or in the stromal nerves during the 3 years following penetrating keratoplasty. Moreover, a grafted cornea obtained 29 years after surgery did not show normal corneal sensitivity: The subepithelial nerve plexus presented with branched nerve fibers, but only a few stromal nerve trunks had regenerated [85].

Richter et al. [70] investigated corneal grafts using a Microphthal confocal microscope and compared the results with those obtained by esthesiometry. In the peripheral graft, the first atypically curved nerve fibers were detected in the middle stroma at 2 months and under Bowman’s membrane at 3 months after surgery. In the central cornea, the first stromal nerve trunks were detected at 7 months after kera-

toplasty, while the first bunches of subepithelial nerve plexus were noted only after 24 months. To date, the results of confocal microscopy appear to correspond to esthesiometry findings.

Confocal microscopy provides insights into the morphological and functional aspects of

corneal reinnervation after surgery. The sample images of corneal innervation after grafting illustrate the structures of the subepithelial nerve plexus and stromal nerves at about 24 months after surgery (Fig. 5.53).

Figure 5.54a–c shows hypertrophy of corneal nerves in a patient with neurofibromatosis.

Fig. 5.53 Reinnervation after penetrating keratoplasty. a Graft center: complete reinnervation of subepithelial nerve plexus 24 months after surgery. b Graft center: incomplete reinnervation of subepithelial nerve plexus; curved nerve bunches 25 months after surgery; dendritic cells. c Graft cen-

ter: nerve trunk in middle stroma 24 months after surgery. d Graft periphery: incomplete reinnervation of subepithelial nerve plexus, hyperreflective scattering at the level of Bowman’s membrane 24 months after surgery

Fig. 5.56 a–f Dots and maplike lesions. a Slit-lamp photograph of dots. b, c Round structures corres-

ponding to microcysts containing hyperreflective material. d Slit-lamp photograph of maplike lesions

a

Fig. 5.57 Reis–Bückler corneal dystrophy.

a Oblique section showing reflective and irregular material at the level of Bowman’s layer and the anterior stroma. b Highly reflective tissue at

the level of Bowman’s layer. c Deposition of fine reflective material in the basal cell layer

b

c

Fig. 5.58 Bowman’s membrane 4 weeks after ammonia burn injury and complete epithelial wound healing with extreme development of a fiber matrix structure

5.5 Stroma

5.5.1

Normal Anatomy

Apart from neural structures, only the highly reflective, sharply demarcated cell nuclei of the keratocytes are visualized on examination of the stroma. The cytoplasm of this fibroblast subpopulation and the collagen fibers produced by them are not visible. Keratocyte nucleus density is higher in the anterior stroma close to Bowman’s membrane than in the central and deep stroma (Figs. 5.59 and 5.60). Keratocyte density is highest in the anterior stroma, clearly declines toward the central stroma, and increases again slightly in the region immediately before Descemet’s membrane.

Fig. 5.61 depicts posterior stroma, and Fig. 5.62 compares normal and activated stroma.

Fig. 5.59 Anterior stroma. In the corneal stroma only the keratocyte nuclei are visualized. Cell nucleus density is highest in the anterior stroma; the cell nuclei shown are approximately 15 µm in diameter

Fig. 5.60 Central stroma. Clearly demarcated, highly reflective, oval keratocyte nuclei in the central stroma; cell nucleus density is lowest in the central stroma

a

b

c

Fig. 5.61 Posterior stroma. Clearly demarcated, highly reflective, oval nuclei, which appear larger and are more numerous than in the central stroma but less numerous than in the anterior stroma. Anterior (a), central (b), and posterior stroma (c)

a

b

Fig. 5.62 Central stroma. a Normal keratocytes. b Activated keratocytes

Fig. 5.64 a–f Penetrating keratoplasty. a Slit-lamp photograph of 72-year-old woman after penetrating keratoplasty. The graft is well located, clear, and fully epithelialized, with small areas of fibrination near the endocorneal suture. b–f Normal epithelial structure

with a number of Langerhans cells (arrow) at the level of the basal cells and subepithelial nerve plexus. Scar areas (d) of basal epithelium in fibrination zones. Nerve fibers are absent both in the epithelium and in the stroma of the graft